Tiny bubbles of IPv4 in future IPv6-only networks

Sometimes I get ideas about things which won't need to exist for a very
long time. That doesn't stop me, of course, so I keep pondering them,
and stir in a dose of reality. The way people operate now when they buy
things in bulk to do some menial job is probably going to be the same in
a few decades. This shapes the ultimate design of my vaporware product
idea.

Let's say it's quite a number of years from now, and people are starting
to set up local networks which are IPv6-only. For whatever reason, they
don't run IPv4 on the same wire. I'm going to assume this will be
rooted in some kind of corporate decree stemming from a shortsighted
technology decision. It's the sort of thing like this: "enabling both
causes X and Y to happen, so we're just going to abandon 4". Someone
will probably push this forward in order to accomplish one of their
quarterly goals.

Just like now, this bulldozing of things in order to make their goal
will overlook something that's been largely forgotten but is rather
important. They will forget that their network includes a number of
old embedded devices which only speak IPv4. These are cameras,
thermostats, door sensors, and so on. They are relatively dumb devices
which have been installed in hard-to-reach places for years and just
keep working.

So now they have a problem. Going to "all 6" is going to leave those
devices useless. That's not an option. They can't exactly go and
replace all of them, because maybe some of them aren't being made any
more (say, for a proximity card technology that's past its prime), and
besides, it would be crazy expensive. They forgot about them, so
they never budgeted for replacing all of them, including the physical
labor of actually reaching some of these things (a variety of
interesting and hard-to-reach places).

They can't stay where they are, but they can't go forward, either. Now
what? Well, they need a solution which will let them go forward while
holding back little pockets of the network in a way that's
nigh-impossible to screw up. It also needs to be affordable.

This is where my idea comes in. Someone will make a little box which
has a pair of RJ45s and some kind of embedded firmware inside. One side
goes to the old device, and one side goes to the new network. For bonus
points, it should be designed with these ports spread to either side of
the device instead being next to each other, and the outer plastic
clamshell should have huge colorful arrows and labels, like
"<--- OLD " and "NEW --->", so it's hard to get wrong. It might
also have a barrel connector or similar for power. If it uses
power-over-Ethernet, then it'll need to also pass that through somehow.

Anyway, inside the box, it'll have just enough brains to join the IPv6
network on the "NEW" side while also creating an entire IPv4 Internet
from whole cloth on the "OLD" side. Its job is going to be to
consistently map any given 128 bit v6 address to a usable 32 bit v4
address inside its "bubble". Then it just has to throw traffic back and
forth.

The consistency in mapping will need to be preserved across multiple
instances of these vaporware devices. That way, you can be sure that
any given v6 address will map to the same v4 address behind all
of these devices. That way, you can just grant access to that on your
cameras, thermostats, or whatever, and that same setting can be applied
universally to your legacy v4-only stuff.

Obviously, when you hash 128 bits down to 32, there will be collisions,
but that's nothing new to this situation. The general goal here is to
ensure that you can use multiple host addresses within a typical
corporate v6 network and still be able to tell them apart within the v4
"bubbles" behind these hypothetical devices.

There is a catch here, of course. This assumes that everything the
original device does works by having other systems connect to it. If
it needs to connect outward for some reason, you're in a world of hurt.
I'm mostly thinking about these cheap "IP cameras" and things of that
nature where they just sit there and wait for something else to connect
and start polling.

I have to admit that part of my inspiration for this device is looking
to tweak the IPv6 wonks who insist that NAT is evil and must never be
allowed to touch their precious addressing scheme. I just have this
feeling that the clammy fingers of reality are going to reach out and
force this issue sooner or later, and devices like I have described
here will be the result.

If this becomes successful, expect to see a small number of web sites
pop up which offer to run the "XYZ calculation" which gives the expected
"bubbled" v4 address from a given v6 address. It's no different from
what happens with corporate technology today: people get stuck running
it, and rely on the results of random web searches to cargo-cult their
way through it.